1. Field of the Invention
This invention relates to a sensor assembly for measuring the weight applied to a vehicle seat.
2. Related Art
Most vehicles include safety devices such as airbags and seatbelt restraint systems, which work together to protect the driver and passengers from experiencing serious injuries due to high-speed collisions. It is important to control the deployment force of the airbags based on the size of the driver or the passenger. When an adult is seated on the vehicle seat, the airbag should be deployed in a normal manner. If there is an infant seat or small adult/child secured to the vehicle seat then the airbag should not be deployed or should be deployed at a significantly lower deployment force. One way to control the airbag deployment is to monitor the weight of the seat occupant.
One system for measuring seat occupant mounts sensors between various structural components on a vehicle seat, such as between an upper seat structural component and a seat riser or the vehicle floor. The sensors are load cells that have a strain gage mounted on a bendable or deflectable body portion that measures the amount of strain in the deflectable body portion resulting from a weight force being exerted on the vehicle seat. The strain measurements from each of the sensors are combined to determine the total weight of the seat occupant.
The system also includes an overload stop formed within the upper seat structural component, which prevents the seat from separating from the vehicle floor or riser under an overload condition. For example, during a high-speed collision, the weight of a seat occupant secured to the seat with a seatbelt exerts an upward force on upper seat structural components. This upward force can cause the seat to separate from the vehicle floor. The overload stop is designed into the seat structural components to prevent this from happening. The overload stop includes a fastener that has one end attached to the vehicle floor with the opposite end having an enlarged head portion extending into the upper structural component of the seat. A predetermined gap is maintained between the bottom of the structural component and the head portion of the fastener. When an overload force is applied, the seat tries to pull away from the floor causing the structural component to move upwardly into engagement with the head portion of the fastener. The enlarged head portion of the fastener prevents the structural component from separating from the floor.
One disadvantage with the current system is that during an overload condition, the bendable body portion can plastically deform or break, resulting in permanent damage to the sensor assembly. To minimize the occurrence of this problem, the predetermined gap size must be very small, i.e., less than two millimeters. This small gap size is difficult achieve and maintain due to dimensional tolerance stack-ups resulting from the assembly of various different components.
Another disadvantage with the current system is that due to the structural mounting configurations and requirements for overload protection in seat assemblies, it is difficult to provide adequate strength for the body portion of the sensor while also providing accurate strain measurements at the lower strain ranges. In other words, because the sensor assemblies are connecting elements between the seat frame member and seat track member, the sensor assemblies must be strong and durable enough to provide secure connection point within the seat assembly but must also be able to provide a sufficient amount of bending/deflection so that the strain gages can measure strain accurately over a wide range of occupant sizes.
Thus, it is desirable to have an improved seat occupant weight measurement system that provides adequate strength, overload protection, and increased accuracy as well as overcoming any other of the above referenced deficiencies with prior art systems.
Weight sensor assemblies for measuring a normal weight force applied to a vehicle seat are installed between an upper seat structure and a vehicle base member such as a riser or vehicle floor. Each sensor assembly includes a plate with a first mount for mounting the beam to the upper seat structure, a second mount for mounting the beam to the vehicle base member, and a center body portion extending between the first and second mounts that exhibits bending behavior during normal weight force applications. A resilient beam member is mounted between each weight sensor assembly and the vehicle base member to prevent sensor failure during an overload force application in a direction opposite to that of a normal weight force application. A strain gage is mounted on the plate at the center body portion to measure the strain caused by the bending. The strain measurements are transmitted to a central processing unit that determines the total weight. The processing unit generates a control signal for a safety device based on the weight determination.
In the preferred embodiment, the resilient beam member is a spring having one end mounted to the vehicle base member and an opposite end mounted to the plate with a spring body portion extending between the first and second spring ends. The spring body portion is spaced apart from the center body portion of the plate to define a gap. There is also a gap between the center body portion of the plate and the upper seat structure. This allows the plate to exhibit S-shaped bending with one portion of the plate being in tension and another portion being in compression.
An overload stop reacts between the vehicle base member and the upper seat structure to prevent seat separation from the vehicle floor during the application of an overload force. The overload stop includes a fastener that is attached at one end to the vehicle floor with an opposite end extending into an opening in the upper seat structure. The fastener includes an enlarged head portion of greater size than the opening that engages the supper seat structure during the application of an overload force.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.